Method and system for additive manufacturing using a light beam

ABSTRACT

The method comprises the steps of: a) supplying building material; and b) fusing the building material using a light beam ( 2 ); wherein steps a) and b) are carried out so as to progressively produce the object out of the fused building material. In step b), the beam ( 2 ) is projected onto the building material so as to produce a primary spot on the building material, the beam being repetitively scanned in two dimensions in accordance with a first scanning pattern so as to establish an effective spot ( 21 ) on the building material, said effective spot having a two-dimensional energy distribution. The effective spot ( 21 ) is displaced in relation to the object being produced to progressively produce the object by fusing the building material.

TECHNICAL FIELD

The present invention relates to the production of three-dimensionalobjects by additive manufacturing.

STATE OF THE ART

Three-dimensional objects can be produced in many ways, such as bymolding in a mold or by removing material from a workpiece, for example,using chipping machines. However, during the last decades, so-calledadditive manufacturing (AM) has become increasingly popular. In additivemanufacturing material is added to an object being produced, so as tobuild up the three-dimensional object. That is, additive manufacturingis based on addition of material rather than on removal of material.

Some AM technologies involve the use of an energy beam which is appliedto a building material so as to fuse the building material. Byprogressively adding up layers of fused building material, thethree-dimensional object is produced. Building materials includepolymers, metals, ceramics and composites, and are often supplied inpowder form. Here, a distinction has to be made between systems using anelectron beam and systems using a light beam, generally a laser beam.

One example of an AM technology is the so-called power bed fusion (PBF)process. PBF processes include one or more thermal sources for inducingfusion between powder particles in a certain region of a powder layercorresponding to a cross-section of the product being formed, and meansfor adding and smoothing powder layers. A well-known example of thiskind of process is the so-called Selective Laser Sintering (SLS)process, where a laser beam fuses a thin layer of powder (for example, alayer of powder having a thickness in the order of about 0.1 mm) in aregion that corresponds to the cross-section of the object to be formed.

The powder is spread across a build area using a counter-rotatingleveling roller, and is preheated to a temperature close to the meltingpoint and/or glass transition temperature of the building material. Thepurpose of the preheating is to reduce the power requirements on thelaser beam. Once the material has been distributed and preheated, afocused laser beam is projected onto the layer of building material, andthe laser spot is displaced over a region of said layer so as toprogressively fuse the material in this region. This region correspondsto a cross-section of the product to be formed, whereby the fusing ofthe building material in this region creates a slice of the product.Next, the building area is lowered and a new layer of building materialis applied, supported by the fused building material and by the powdersurrounding it. By repeating these steps, the product is built up sliceby slice, until it is finished. There are at least four different fusionmechanisms that are used in PBF processes, namely: solid-statesintering, chemically-induced sintering, liquid-phase sintering and fullmelting. In commercially used processes, liquid-phase sintering andmelting tend to dominate. Examples of SLS processes and systems aredisclosed in US-2014/0079916-A1 and U.S. Pat. No. 6,215,093-B1.

Another AM technology involving the use of electromagnetic energy beams(typically laser beams) is the so-called beam deposition (BD) process.In this kind of process, the building material is heated while it isbeing deposited, by applying an energy beam to the building material.Whereas in the PBF process described above the building material isfirst deposited in a layer and then selectively heated by the energybeam, in BD processes the material is being heated and melted as it isbeing deposited. BD processes include laser-based metal deposition(LBMD) processes, typically involving a deposition head integrating oneor more powder nozzles and laser optics. The process involves controlledrelative movement between the deposition head and a substrate, by movingthe deposition head, the substrate, or both. An example of a beamdeposition system is disclosed in US-2012/0138258-A1. Examples of powderdeposition nozzles are disclosed in US-2014/0015172-A1 and inWO-2008/003942-A2.

US-2013-0168902-A1 discloses a powder bed fusion system in which themelting area is detected by a sensor device, for the purpose of qualitycontrol.

US-2012/0266814-A1 describes how in order to deposit a relatively widecoating, this must be done by overlapping a series of clads side byside. It is explained that if only the laser beam diameter is increased,then the temperature at the center of the melt pool is such that highlevels of vaporization of additive material may occur, or the substratemay melt to an excessive depth. Further, the surrounding substratematerial may be disrupted to an excessive depth, etc. The documentdescribes a system in which the laser beam is shaped in a beam shapingapparatus involving a plane mirror and a diffractive optical element, soas to provide for beam energy distribution different from thetraditional Gaussian one, to improve the process. For example, theintensity can be arranged to be relatively high at the leading edge ofthe laser spot, or at the edges of the laser spot.

US-2013/0300035-A1 discloses a powder bed fusion system and emphasizesthe need to control the temperature of the irradiated building materialin order to avoid geometrical deformations and cracks and to assurethorough fusion. It also mentions the need to reduce production time andthe need to sweep the beam as efficiently as possible over the selectedarea. It mentions how a scan pattern can be used having parallel linesand how there is a need to take into account heat from previouslyscanned lines, which can be done by varying beam power or speed. Thedocument proposes a method involving calculations related to anestablished beam path and an imaginary beam. The invention disclosed inthis document relates to a method where the energy deposition of thebeam to be used can be pre-adjusted based on calculations.

US-2011/0305590-A1 discloses a beam deposition arrangement where, in oneembodiment, laser radiation is processed so as to generate a relativelyhigh intensity region used to consolidate the powder, and a relativelylow intensity region used to heat a substrate to mitigate distortion ofthe substrate during fabrication.

Generally, fusing of the selected region or portion of a layer isobtained by scanning the laser beam over the region following a beampath, so that the laser spot projected onto the layer is displaced overthe surface of the layer to subsequently heat different portions of theregion, typically a plurality of parallel tracks, until the entireregion has been heated and fused to the desired extent.US-2004/0099996-A1 teaches an example of how radiation energy is appliedin tracks. US-2006/0215246-A1 discloses how there are two types of laserscanning commonly performed in rapid-prototyping systems: rasterscanning and vector scanning. US-2004/0200816-A1 also teaches thatraster scanning and/or vector scanning were used to fill the area to befused, for example, by fusing the powder along an outline of the crosssection in vector fashion either before or after a raster scan thatfills the area. This document suggests the use of a thermal imagefeedback for controlling temperature, for example, by controlling beampower and/or scan speed.

US-2003/0127436-A1 teaches a way of reducing the build time of anarticle by reducing the number of raster scan lines required for eachcross-section of the article.

US-2003/0028278-A1 teaches raster scanning with a selected line-to-linedistance between scans, with the location of the scan linessubstantially centered between the locations of the scan lines in theprevious layers. Thereby, the number of scans required for the formationof an article can be reduced, without degrading the structural strength.

DE-10112591-A1 teaches some alternative laser scanning patterns in thecontext of additive manufacturing.

U.S. Pat. No. 5,904,890-A teaches adapting the speed with which thelaser beam and laser spot are displaced along the lines of the scanningpattern, depending on the length of the lines, in order to achieve amore homogeneous density distribution.

US-2013/0216836-A1 teaches, in the context of a melting/sinteringprocess, the use of a non-linear scanning path to reduce the time forthe beam of the electromagnetic radiation source to traverse an area.

US-2014/0154088-A1 teaches the relation between secondary grainorientation and scanning pattern of an energy beam.

DE-102009015282-A1 teaches the application of different amounts ofenergy to different portions of the layer that is being selectivelysintered or melted, based on a function or on data in a table. Thereby,the mechanical characteristics of the product can be improved.

US-2011/0168090-A1 and US-2011/0168092-A1 teach laser depositionapparatuses having wide spray nozzles, so that a relatively wide coatingof uniform thickness can be deposited. The wide nozzles are combinedwith a wide laser beam, which can be obtained by means of beammanipulation techniques such as, for example, scanning.

US-2010/0036470-A1 discloses processes for laser based fabrication ofelectrodes and mentions process control by parameters including laserenergy and laser spot size. US-2008/0296270-A1 discloses direct metaldeposition using a laser and powder nozzle, with a control system forcontrolling process parameters including laser power and traverse speed.Also laser beam power is mentioned as a process parameter.US-2006/0032840-A1 teaches the adaptation of the laser power based onfeedback control. US-2009/0206065-A1 teaches selected laser powderprocessing with adjustment of process parameters including laser powerand/or laser spot size. US-2002/0065573-A1 mentions parameters such aslaser power, beam diameter, temporal and spatial distribution of thebeam, interaction time, and powder flow rate. The document proposes theuse of a diode laser for rapid response and fine tuning to the processat a fast rate.

WO-2014/071135-A1 teaches, in the context of additive manufacturing, theconcept of appropriately modulating a laser beam pulse to accurately andprecisely control the amount of heat applied to a powder material,particularly for the purpose of achieving much finer control of thecharacteristics of the final object produced by the method.

US-2006/0119012-A1 teaches a method for producing parts using lasersintering wherein a fusible powder is exposed to a plurality of laserscans at controlled energy levels and for time periods to melt anddensify the powder.

CN-1648802-A discloses the use of a high energy beam to sinter or meltand deposit material successively. The document appears to teach fastscanning using an electron beam. Through one or several frames ofscanning, the material in the forming area has its temperaturesynchronously raised to reach the sintering or re-melting temperaturefor deposition onto the forming area before synchronous cooling. This isbelieved to reduce heat stress and raise forming precision and quality.

US-2010/0007062-A1 discloses homogeneously preheating powder material byscanning with a high energy beam along predetermined paths over apre-heating area.

DE-10208150-B4 teaches that the roughness of the surface of the objectbeing produced can be reduced by letting the laser beam scanning thecorresponding portion of the powder layer oscillate back and forth inthe direction of its general movement along the track, thereby heatingthe same portion several times. The document also teaches that amovement in the lateral direction can be added to this movement in thelongitudinal direction of the track, for the purpose of setting orvarying the width of the track. The method including the movement of thelaser spot forth and back along the track can also be used for otherparts of the layer being fused, not only for the one defining thesurface of the object. The speed, size or power of the laser spot can bemodified during this movement forth and back. The document indicatesthat the laser can create moving Lissajous figures.

US-2003/0075529-A1 discloses the use of adjustable focusing optics tocontrol the beam geometry in the context of a beam deposition process.Parameters such as road width and intensity distribution can becontrolled. A vibrating or oscillating element can be used so that theroad width can be determined by adjusting the amplitude of theoscillation.

US-2001/0002287-A1 teaches the use of beam shaping optics to createnon-symmetric laser beams, including laser beams with a leading portionhaving a higher laser beam intensity than a trailing portion, imposing athermal gradient upon the deposited material during re-solidification.

US-2012/0267345-A1 teaches how, in the context of additivemanufacturing, the cross sectional shape of the laser beam is adjustedduring the process to control the distribution of energy, using adeformable reflective means such as a deformable mirror.

Not only a laser beam but also an electron beam can be used for additivemanufacturing. However, in the case of an electron beam, the crosssection of the beam cannot be shaped using optics in the same way aswith a laser beam, and a different approach has to be taken.WO-2004/056509-A1 teaches inter alia the use of an electron beam forproducing a three-dimensional object, and suggests the use of aninterference term in order to provide a more favorable heat distributionin an area around the focal point or to provide for a widened trace. Theuse of a movement with a component in a direction perpendicular to themain movement direction may be especially advantageous in the context ofan electron beam, in order to provide for some kind of effective heatedspot being wider than the focal point of the electron beam, that is,similar to what can be achieved by using appropriate optics when theenergy beam is a laser beam. Scanning an electron beam to create more orless complex figures is well known in the art, cf. for example how thisconcept has been implemented for decades in cathode ray tubes. It iswell known in the art to control the direction of electron beams usingmagnetic fields, without the need for physical displacement ofcomponents.

As explained in, for example, US-2002/0145213-A1, selective lasersintering has traditionally been based on a spot by spot or point bypoint approach. US-2002/0145213-A1 suggests a different technique, basedon the creation of transferable powder toner images of a binding powderand at least a modifier powder in accordance with the corresponding CADdesign. The build-up of the object takes place area by area, instead ofpoint by point.

US-2008/0038396-A1 teaches the production of three-dimensional objectsby solidification of a building material using electromagneticradiation. The energy input is via an imaging unit comprising apredetermined number of pixels.

US-2003/0052105-A1 suggests a pixel approach for laser sintering,including, for example, the use of a digital micromirror device.

US-2002/0051853-A1 discloses production of an object layer by layer,using a single laser beam to outline the features of the object beingformed, and then a series of equally spaced laser beams to quickly fillin the featureless regions, thereby speeding up the process.

WO-2014/016402-A1 discloses a device comprising a galvanometric headable to steer a laser beam toward each point of a maximum sintering zoneof a sintering field when said galvanometric head is positioned at apredetermined position. The device further comprises limiting means ableto limit the steering of the laser beam to an effective sintering zonesituated inside said maximum sintering zone, and movement means formoving said galvanometric head in a plane parallel to the plane of saidsintering field, allowing said galvanometric head to be positioned at atleast two different positions, an effective sintering zone beingassociated with each position of said galvanometric head.

CN-103567441-A discloses a method for laser sintering wherein the sizeof the laser spot is modified during the process to speed up theprocess.

CN-203227820-U discloses a method wherein the size of the laser spot ismodified during the process to adapt the size to the width of thecomponent being manufactured.

U.S. Pat. No. 5,753,171-A teaches the use of a variable focusing devicewhereby the focus of the light beam can be varied during solidificationof a layer, so that different parts of the layer are subjected to heattreatment with different beam diameters.

WO-2014/006094-A1 discloses a method comprising a step of acquiring thegeometric outline of a two-dimensional section to be fused; a step ofdetermining a reference path from said geometric outline of the section,said reference path having a shape that is correlated with the shape ofsaid geometric contour; a step of determining a set of paths on thebasis of said reference path; and a step of controlling the laser beamsuch that it moves along the set of predetermined paths according to amoving strategy defining an order of the paths along which to move, and,for each path, a point from which to start moving. This method aims atenhancing productivity.

US-2013/0270750-A1 acknowledges that process speed cannot be increasedsimply by increasing power and/or scanning speed: increased power canend up producing vaporization, whereas increased scanning speed reducesthe dwell time which may end up being too short. This document suggestsan approach based on the simultaneous use of two laser beams.

US-2005/0186538-A1 teaches that the production time can be reduced whenthe energy of a high-energy beam is coupled into the material in aplurality of steps. In the first step, the energy is coupled into acertain position in the layer of material until the respective portionof the layer at said position has been heated to a temperature justbelow its melting point. In the final step of coupling in energy, thebeam then heats said portion above the melting point, thereby fusing thematerial to the layer below it. In this way, the product being made isformed.

WO-2013/079581-A1 discloses how the energy input per unit time can bevaried as a function of the respective irradiation site on the powderlayer, taking into account the heat removal capability of a defineddirectly surrounding region. Energy input is appropriately modulatedautomatically by setting of the irradiation parameters such as energydensity of the radiation at the irradiation site and/or duration of theirradiation of the irradiation site.

DE-10320085-A1 relates to laser sintering or laser melting processes anddiscusses adaptation of the laser heating by adapting features such aspower density, scanning speed, width of the track, distance between thetracks, laser beam diameter, and beam power, during the production of anobject.

US-2004/0094728-A1 discloses a system in which the scanner is moveableabove a platform on which the object is being formed, so as allow forthe production of large objects with good quality.

WO-2014/037281-A2 discloses a method and system for laser hardening ofthe surfaces of workpieces, with a special focus on crankshafts. Laserhardening of steel is a well-known concept, but some workpieces areproblematic due to the presence of more heat sensitive regions which cansuffer damage when heated by the laser beam. For example, in the case ofcrankshafts, a problem resides in the presence of more heat sensitiveportions such as the areas adjacent to the oil lubrication holes.WO-2014/037281-A2 teaches how this and similar problems can be overcomeby using an effective laser spot with a two-dimensional energydistribution that can be dynamically adapted to avoid overheating of themore heat sensitive subareas.

DESCRIPTION OF THE INVENTION

A first aspect of the invention relates to a method for producing anobject, the method comprising the steps of:

-   a) supplying building material; and-   b) fusing the building material using a light beam;

wherein steps a) and b) are carried out so as to progressively producethe object out of the fused building material;

wherein in step b), the beam is projected onto the building material soas to produce a primary spot on the building material, the beam beingrepetitively scanned in two dimensions in accordance with a firstscanning pattern so as to establish an effective spot on the buildingmaterial, said effective spot having a two-dimensional energydistribution,

and wherein said effective spot is displaced in relation to the objectbeing produced to progressively produce the object by fusing thebuilding material.

The building material can be any building material suitable for additivemanufacturing by fusion by heat applied with a light beam, such as alaser beam. In many embodiments of the invention, the building materialis supplied in powder form. In many embodiments of the invention, thebuilding material is selected from the group comprising metals,polymers, ceramics and composites, and mixtures or combinations thereof.

The term fuse (fusing, etc.) should not be interpreted narrowly andencompasses any alteration of the supplied building material suitablefor manufacturing an object out of it. In the present document, theconcept “fusion” encompasses fusion mechanisms such as solid-statesintering, chemically-induced binding, liquid-phase sintering and fullmelting.

The light beam is a beam of electromagnetic radiation, for example, alaser beam. The effective laser spot can be created and adapted using,for example, any of the techniques described in WO-2014/037281-A2, whichis incorporated herein by reference. Whereas WO-2014/037281-A2 isfocused on the laser hardening of previously produced workpieces, suchas crankshafts, featuring heat-sensitive subareas such as the areasadjacent to the oil lubrication holes, it has been found that theprinciples disclosed therein regarding the scanning of the laser beamcan be applied also to the area of additive manufacturing, where theycan be used to enhance the manner in which building material is fused,in terms of velocity and/or quality.

In some embodiments of the present invention, the method is implementedas a powder bed fusion method, for example, as an SLS (Selective LaserSintering) method. In other embodiments of the invention, the method isimplemented as a beam deposition method, for example, as a laser beamdeposition method.

The displacement of the effective spot in relation to the object beingproduced can be carried out in accordance with a second scanningpattern. That is, the real/primary spot, that is, the spot that isproduced by the beam at any given moment, is scanned in accordance witha first scanning pattern to create the effective spot, and thiseffective spot can be displaced in accordance with the second scanningpattern. Thus, two types of movement are combined or overlaid: themovement of the primary spot in accordance with the first scanningpattern, and the movement of the effective spot in accordance with thesecond scanning pattern.

The term “two-dimensional energy distribution” refers to the manner inwhich the energy applied by the energy beam is distributed over theeffective spot, for example, during one sweep of the beam along thefirst scanning pattern.

The present invention allows for a relatively rapid fusion of asubstantial area, due to the fact that the effective spot can have asubstantial size, such as, for example, more than 4, 10, 15, 20 or 25times the size (area) of the primary spot. Thus, heating a certainregion or area of the building material to achieve fusion can beaccomplished more rapidly than if the heating is carried out by simplydisplacing the primary spot over the entire area, for example, followinga scanning pattern made up of a plurality of parallel lines, arrangedclose to each other. The use of an effective spot having a relativelylarge area allows for high productivity while still allowing eachportion of the building material to be heated for a relativelysubstantial amount of time, thereby allowing for less aggressive heatingwithout compromising productivity. The primary spot can have an areasubstantially smaller than the one of the effective spot. For example,in some embodiments of the invention, the primary spot has a size ofless than 4 mm², such as less than 3 mm², at least during part of theprocess. The size of the primary spot can be modified during theprocess, so as to optimize the way in which each specific portion of theobject is being formed, in terms of quality and productivity.

On the other hand, the use of an effective spot created by scanning theprimary spot repetitively in two dimensions in accordance with a firstscanning pattern, makes it possible to establish an effective spothaving a selected two-dimensional energy distribution, which issubstantially independent of the specific optics (lenses, mirrors, etc.)being used, and which can be tailored and adapted to provide for anenhanced or optimized fusion of the building material and production ofthe object, from different points of view, including the speed withwhich the production takes place in terms of kg or units per hour, andquality. For example, the heat can be distributed so that a leadingportion of the effective spot has a higher energy density than atrailing portion, thereby increasing the speed with which fusion isinitiated, whereas the trailing portion can serve to maintain the fusionfor a sufficient time to reach a desired depth and/or quality, therebyoptimizing the velocity with which the effective spot can be displacedin relation to the object being produced, without renouncing on thequality of the fusion. Also, the two-dimensional energy distribution canbe adapted in relation to the sides of the effective spot, depending onthe characteristics of the building material or object at these sides,for example, so as to apply less heat in areas where the buildingmaterial already features a relatively high temperature, for example,due to heating that has taken place recently, for example, during apreceding sweep of the effective spot in correspondence with an areaadjacent to the one currently being heated. Also, the effective spot canbe adapted in accordance to the shape of the object being formed, forexample, the effective spot can be made thinner (that is, less wide) orwider in a direction such as the lateral direction (that is, thedirection perpendicular to the direction in which the effective spot isbeing displaced along the second scanning pattern) when this is neededfor the fusion of the building material in a certain area of the objectbeing produced, for example, to correspond to the width of the portionof the object being produced in that area. For example, in someembodiments of the invention, the width of the effective spot can bedynamically adapted to match the respective dimension (such as width) ofthe respective portion of the object being produced at the differentpositions along a track along which the effective spot is swept, whilethe effective spot is swept along the track. Actually, not only thegeneral or average width of the effective spot but also the shape of theeffective spot, such as the way in which the width of the effective spotvaries along the length of the effective spot, can be dynamicallyadapted, for example, to correspond to the shape of the respectiveportion of the object being formed at each moment. For example, thetwo-dimensional energy distribution can be adapted so that theprojection of the effective spot onto the building material features ashape adapted to the shape of the object being formed, for example, toadopt a wedge-shape or similar in correspondence with a narrowingportion of the object being formed, etc.

The shape of the effective spot and/or the two-dimensional energydistribution can be adapted whenever needed, thereby adapting theprocess to the specific object that is being produced, and to thespecific part of the object that is being produced at any given moment.In some embodiments of the invention, the two-dimensional energydistribution can be varied as a function of the respective irradiationsite on the powder layer, taking into account the heat removalcapability of a surrounding region. In some embodiments of theinvention, the two-dimensional energy distribution can be varied takinginto account desired characteristics of the product in different regionsof the product, such as different requirements on porosity and/orhardness, for example, depending on the distance to a surface of theproduct. This can be useful in order to speed up sintering of areasrequiring less hardness, thereby enhancing productivity.

Additionally, using the effective spot, created by the scanning of theprimary spot in two dimensions, increases flexibility in terms of, forexample, adaptation of a system to different objects to be produced. Forexample, the need to replace or adapt the optics involved can be reducedor eliminated. Adaptation can more frequently be carried out, at leastin part, by merely adapting the software controlling the two-dimensionalenergy distribution of the effective spot.

The expression “first scanning pattern” does not imply that the primaryspot must always follow one and the same scanning pattern when creatingthe effective spot, but is merely intended to distinguish the scanningpattern of the primary spot that is used to create the effective spot,from the pattern with which the effective spot is displaced or scannedin relation to the object being produced; the scanning pattern followedby the effective spot is sometimes referred to as a second scanningpattern.

In many embodiments of the invention, the velocity or mean velocity withwhich the primary spot is displaced in accordance with the firstscanning pattern is substantially higher than the velocity with whichthe effective spot is displaced in relation to the object. A highvelocity of the primary spot along the first scanning pattern reducesthe temperature fluctuations within the effective spot during each sweepof the primary spot along the first scanning pattern.

In prior art systems, the melt pool or pool, that is, the area or regionwhere fusion is taking place, substantially corresponds to the primaryspot projected by the beam on the building material. That is, in priorart systems, the so-called melt pool where the building material isbeing fused generally has a size that substantially corresponds to theone of the primary spot, and the pool is displaced in accordance withthe displacement of the primary spot, for example, along thecircumference of a region to be fused, along raster scan lines fillingan area where building material is to be fused, or along a line wherebuilding material is being deposited in a beam deposition process.Contrarily, in accordance with the present invention, the pool rathercorresponds to the effective spot, or to a substantial portion thereof.For example, in many embodiments of the invention, the pool has a widthsubstantially corresponding to the width of the effective spot (in adirection perpendicular to the direction in which the effective spot isbeing displaced), and the pool is generally displaced in accordance withthe displacement of the effective spot. That is, rather than beingdisplaced in accordance with the displacement of the primary spotfollowing the first scanning pattern, the pool is displaced according tothe displacement of the effective spot, such as following the secondscanning pattern.

Of course, the present invention does not exclude the possibility ofcarrying out part of the fusion process operating with the primary spotin a conventional way. For example, the primary spot can be displaced tocarry out the fusion in correspondence with the outline or contour of aregion to be fused, or to carry out fusion in correspondence withcertain details of the object being produced, whereas the effective spotdescribed above can be used to carry out the fusion of other parts orregions, such as the interior or main portion of a region to be fused.The skilled person will chose the extent to which the effective spotrather than the primary spot will be used to create the pool, dependingon issues such as productivity and the need to carefully tailor theoutline of a region to be fused or a certain portion of an object beingproduced. For example, it is possible to use the primary spot to outlinea region to be fused and to fuse the boundary between this region andthe regions where the building material is not to be fused, while theeffective spot is used it to fuse the building material within theoutlined region. In some embodiments of the invention, during theprocess, the first scanning pattern can be modified to reduce the sizeof the effective spot until it ends up corresponding to the primaryspot, and vice-versa.

That is, it is not necessary to use the effective spot to carry out allof the fusion that has to take place when producing the object. However,at least part of the fusion of building material is carried out usingthe effective spot described above. For example, it can be preferredthat when producing an object, during at least 50%, 70%, 80% or 90% ofthe time during which the beam is applied to the building material, itis applied so as to establish the effective spot of the invention.

In some embodiments of the invention, the two-dimensional energydistribution of the effective spot is dynamically adapted duringdisplacement of the effective spot in relation to the object beingproduced. Thereby, adaptation of the effective spot to the area orregion of the object currently being produced can be accomplished. Theexpression dynamic adaptation is intended to denote the fact thatadaptation can take place dynamically during displacement of theeffective spot, that is, “in-process”, without interrupting the processto, for example, switch between different optics, and without switchingbetween different light beams. Different means can be used to achievethis kind of dynamic adaptation, some of which are mentioned below. Forexample, in some embodiments of the invention, the scanning system canbe operated to achieve the dynamic adaptation (for example, by adaptingthe operation of galvanic mirrors or other scanning means, so as tomodify the first scanning pattern and/or the velocity of the primaryspot along the scanning pattern or along one or more segments orportions thereof), and/or the beam power and/or the size of the primaryspot can be adapted. Open-loop or closed-loop control can be used forcontrolling the dynamic adaptation. The dynamic adaptation can affectthe way in which the energy is distributed within a given area of theeffective laser spot, and/or the actual shape of the effective laserspot, and can often affect the size and/or shape of the pool. Forexample, the length of the effective spot (for example, along thedirection of movement of the effective spot) and/or the width of theeffective spot (for example, perpendicularly to the direction ofmovement of the effective spot) can be adapted dynamically during theprocess, and/or “holes” (that is, areas where no energy or only verylittle energy is applied) can be established within the effective spotin correspondence with areas where no fusion of the building material isdesired. The size and shape of the pool can be determined by thetwo-dimensional energy distribution.

In some embodiments of the invention, the two-dimensional energydistribution of the effective spot is dynamically adapted duringdisplacement of the effective spot along a track, for example, to adaptthe width of the effective spot to a corresponding dimension of aportion of the object being produced.

In some embodiments of the invention, the dynamic adaptation takes placeonce or a plurality of times, for example, continuously, during a sweepof the effective spot along a track, such as along the second scanningpattern or a portion thereof, for example, along a straight or curvedportion of the second scanning pattern. For example, the width of theeffective spot can be adapted one or more times, such as continuously,during a sweep of the effective spot along said track, such as along astraight or curved portion of the second scanning pattern.

In some embodiments of the invention, adaptation of the two-dimensionalenergy distribution of the effective spot is carried out by adapting thepower of the beam, such as by selectively turning the beam on and off.This includes interruption of the beam at its source, as well as otheroptions such as interruption of the beam by interference with the pathof the beam, for example with a shutter, and combinations thereof. Forexample, when using a laser such as a fiber laser, the laser beam can beswitched on and off very rapidly, thus making it possible to obtain adesired energy distribution by turning the laser beam on and off whilefollowing the scanning pattern. Thus, heating can be achieved by turningthe laser beam on during certain lines or parts of lines of the scanningpattern. For example, a pixelized approach can be adopted, according towhich the two-dimensional energy distribution is determined by theon/off state of the laser during the different portions or segments ofthe first scanning pattern.

In some embodiments of the invention, adaptation of the two-dimensionalenergy distribution of the effective spot is carried out by adapting thefirst scanning pattern.

In some embodiments of the invention, adaptation of the two-dimensionalenergy distribution of the effective spot is carried out by adapting thevelocity with which the primary spot moves along at least a portion ofthe first scanning pattern.

That is, the two-dimensional energy distribution can be adapted byadapting, for example, the power of the beam—for example, by switchingbetween different power states such as between on and off-, and/or byadapting the scanning pattern—for example, adding or leaving outsegments, or modifying the orientation and/or the length of segments, orcompletely changing a pattern for another one-, and/or by adapting thevelocity with which the beam moves along the scanning pattern, such asalong one or more segments thereof. The choice between different meansfor adapting the two-dimensional energy distribution can be made basedon circumstances such as the capacity of the equipment to rapidly changebetween power states of the beam, and on the capacity of the scanner tomodify the pattern to be followed and/or the speed with which theprimary spot moves along the scanning pattern.

In some embodiments of the invention, focus of the beam is dynamicallyadapted during displacement of the primary spot along the first scanningpattern and/or during displacement of the effective spot in relation tothe object being produced. For example, the focus of the light beamalong the optical axis can be dynamically modified during the process,for example, so as to vary or maintain the size of the primary spotwhile it is being displaced along the first scanning pattern, and/orwhile the effective laser spot is being displaced in relation to theobject being produced. For example, the optical focus can be adapted tokeep the size of the primary spot constant while the primary spot ismoving over the surface of the object being produced (for example, tocompensate for varying distances between the scanner and the position ofthe primary light spot on the object being produced).

In some embodiments of the invention, the size of the primary spot isdynamically adapted during displacement of the primary spot along thefirst scanning pattern and/or during displacement of the effective spotin relation to the object being produced, so as to modify thetwo-dimensional energy distribution and/or the size of the effectivespot.

In some embodiments of the invention, during at least one stage of themethod, the effective spot comprises a leading portion having a higherenergy density than a trailing portion of the effective spot (thisarrangement can be preferred when it is desired to rapidly reach acertain temperature, and thereafter provide sufficient energy input to,for example, keep the material at the required temperature for a certainamount of time), or the effective spot comprises a leading portionhaving a lower energy density than a trailing portion of the effectivespot (this arrangement can be preferred when it is desired to firstpre-heat the material for some time, prior to making it reach a certaintemperature, such as the one at which fusion of the building materialtakes place). In some embodiments of the invention, the effective spotcomprises an intermediate portion having a higher energy density than aleading portion and a trailing portion of the effective spot. In someembodiments of the invention, the effective spot features asubstantially uniform energy distribution, with a substantially constantenergy density throughout the effective spot.

As indicated above, the two-dimensional energy distribution can beadapted dynamically while the method is being carried out, for example,so that it is different in relation to different portions of the objectthat is being produced, and this adaptation can be carried out not onlyat a beginning and/or at an end of a track followed by the effectivespot, but also within the track. For example, the two-dimensional energydistribution can be dynamically adapted in accordance with the shape ofthe portion of the object being formed at each moment, for example, as afunction of the width of the portion to be formed, taking into accountholes or openings in the object being formed, etc.

In some embodiments of the invention, the mean velocity of the primaryspot along the first scanning pattern is substantially higher than themean velocity with which the effective spot is displaced in relation tothe object being produced. For example, the mean velocity of the primaryspot along the first scanning pattern can preferably be at least tentimes higher, more preferably at least 100 times higher, than the meanvelocity with which the effective spot is displaced in relation to theobject being produced. A high velocity of the primary spot reduces thetemperature fluctuations within the effective spot during one sweep ofthe primary spot along the first scanning pattern.

In some embodiments of the invention, the beam is scanned in accordancewith said first scanning pattern so that said first scanning pattern isrepeated by the beam with a frequency of more than 10, 25, 50, 75, 100,150, 200 or 300 Hz (i.e., repetitions of the scanning pattern persecond). A high repetition rate can be appropriate to reduce or preventnon-desired temperature fluctuations in the areas being heated by theeffective spot, between each scanning cycle, that is, between each sweepof the beam along the first scanning pattern. In some embodiments of theinvention, the first scanning pattern remains constant, and in otherembodiments of the invention, the first scanning pattern is modifiedbetween some or all of the sweeps of the beam along the scanningpattern.

In some embodiments of the invention, the size (that is, the area) ofthe effective spot, such as the mean size of the effective spot duringthe process or the size of the effective spot during at least one momentof the process, such as the maximum size of the effective spot duringthe process, is more than 4, 10, 15, 20 or 25 times the size of theprimary spot. For example, in some embodiments of the invention, aprimary spot having a size in the order of 3 mm² can be used to createan effective spot having a size of more than 10 mm², such as more than50 or 100 mm². The size of the effective spot can be dynamicallymodified during the process, but a large mean size can often bepreferred to enhance productivity, and a large maximum size can beuseful to enhance productivity during at least part of the process, forexample, when producing/fusing large internal areas of an object beingproduced.

In some embodiments of the invention, steps a) and b) are carried outrepeatedly in a plurality of cycles, wherein each cycle comprises:

-   -   carrying out step a), supplying the building material as a        layer;    -   carrying out step b) so as to fuse the building material in a        region of said layer, said region corresponding to a cross        section of the object being produced.

Thereby, using this approach, the object grows slice by slice, eachslice having a thickness corresponding to the thickness of the fusedportion of the layer. For example, this embodiment can encompass theimplementation of the invention as a powder bed fusion process, forexample, as an SLS process. The building material can, for example, beplaced on a platform, which is displaced downwards a distancecorresponding to the thickness of the fused region, each time step b)has been carried out. The building material can be in powder form and bedistributed in a layer having a predetermined thickness using, forexample, a counter-rotating powder leveling roller.

In some embodiments of the invention, steps a) and b) are carried out inparallel, so that the building material is fused by the effective spotas it is being supplied, providing for a continuous progressive growthof the object being produced. This option encompasses beam depositionprocesses. For example, the building material can be supplied in powderform and heated by the beam so as to melt, forming a melt pool. Theobject being produced or a substrate on which it is to be produced canbe moved relative the laser beam whilst the building material continuesto be delivered, whereby a trail of the melted building material isformed, cools and solidifies.

The method can be carried out under the control of a computer, withinput data including those defining the structure of the object to beproduced, for example, CAD data related to the structure of the objectto be produced.

In some embodiments of the invention, the first scanning pattern is apolygonal scanning pattern comprising a plurality of lines. For example,the first scanning pattern can be a polygon such as a triangle, a squareor a rectangle, a pentagon, a hexagon, a heptagon, an octagon, etc. Thepolygon does not need to be a perfect polygon, for example, the linesmaking up the polygon can in some embodiments be more or less curved andthe edges of the polygon where the lines meet can be rounded, etc.

In some embodiments of the invention the first scanning patterncomprises a plurality of lines, such as a plurality of straight orcurved lines, which in some embodiments of the invention are arrangedsubstantially parallel with each other. In some embodiments of theinvention, there are two, three, four or more of these lines.

In some embodiments of the invention, the first scanning patterncomprises at least three segments, and said scanning of the energy beamis carried out so that said beam or spot follows at least one of saidsegments more frequently than it follows at least another one of saidsegments. This arrangement is advantageous in that it enhancesflexibility and the way in which the scanning pattern can be used toprovide an adequate and, whenever desired, symmetric or substantiallysymmetric energy distribution. For example, one of said segments can beused as a path or bridge followed by the beam when moving between twoother segments, so that the transfer of the spot projected by the beambetween different portions (such as an end and a beginning) of the firstscanning pattern can be carried out using segments (such as intermediatesegments) of the scanning pattern for the transfer, whereby the transfercan often be carried out without turning off the beam and withoutdistorting the symmetry of the two-dimensional energy distribution, whensuch symmetry is desired.

In some embodiments of the invention, the first scanning patterncomprises at least three substantially parallel straight or curved linesdistributed one after the other in a first direction, said linesgenerally extending in a second direction, wherein said at least threelines comprise a first line, at least one intermediate line, and a lastline arranged one after the each other in said first direction, whereinsaid scanning of the beam is carried out so that said beam or spotfollows said intermediate line more frequently than said beam followssaid first line and/or said last line. That is, for example, the beamcan on an average follow said intermediate line twice as often as itfollows said first line and said last line, for example, the beam cantravel along the intermediate line each time it moves from the firstline towards the last line, and vice-versa. That is, the intermediateline or lines can serve as a kind of bridge followed by the projectedspot when moving between the first and the last line.

This arrangement has been found to be practical and easy to implement,and it has been found that adequate energy distributions can often beobtained by adapting scanning speed and without substantially adaptingthe power of the beam. It is also possible to modify the power of thebeam during scanning so as to tailor the energy distribution, but rapidswitching of the power is not always possible or desirable, and havingthe beam, such as a laser beam, at a low power level or switched offduring substantial parts of the scanning cycle may imply a sub-optimaluse of the capacity of the equipment, which can be a seriousdisadvantage when the equipment, such as a laser equipment, is used foradditive manufacturing. Thus, it is often desirable to operate with thebeam fully in the on state, to take full advantage of the availablepower.

It is often desirable to use three or more lines arranged in this way,that is, one after the other in a direction different from, such asperpendicular to, the direction along which the lines extend, in orderto achieve a substantial extension of the effective spot not only in thedirection along the lines, but also in the other direction, so as tomake the effective spot adequate for heating a sufficiently wide area toa sufficiently high temperature and to maintain the temperature at thedesired level or levels during sufficient time, while allowing theeffective spot to travel with a relatively high speed, thereby allowingfor a high productivity. Thus, a substantial extension of the effectivespot in two dimensions is often an advantage.

In some embodiments of the invention, the first scanning patterncomprises at least three substantially parallel lines or segments,distributed one after the other in a first direction, such as in thedirection along which the effective spot travels during the process,said lines extending in a second direction, such as in a directionperpendicular the first direction. In some embodiments of the invention,said at least three lines comprise a first line, at least oneintermediate line, and a last line, arranged after each other in saidfirst direction, and the scanning of the beam is carried out so that theprojected spot is scanned along said lines according to a sequence inaccordance with which the spot, after following said first line, followssaid intermediate line, said last line, said intermediate line, and saidfirst line, in that order.

The above definition does not mean that the scanning has to start withthe first line, but just indicates the sequence according to which thebeam tracks or follows the above-mentioned lines of the scanningpattern. Also, it does not exclude that in between (such as before orafter) following some or all of the lines indicated above, the beam mayfollow other lines, such as lines interconnecting the first, last andintermediate lines, and/or additional intermediate lines.

That is, in these embodiments, after moving along the first line, thebeam always follows said intermediate line twice before moving along thefirst line again. Whereas a more straight-forward approach might havebeen to carry out the scanning so that after said last line the beam andits projected spot return directly to said first line, it has been foundthat the sequence followed according to these embodiments of theinvention is suitable to achieve a symmetric energy distribution aboutan axis of symmetry extending in said first direction.

In some embodiments of the invention, the scanning pattern comprises aplurality of said intermediate lines. The number of lines can be chosenby the operator or process designer or equipment designer depending on,for example, the size of the primary spot projected by the beam and thedesired extension of the effective spot, for example, in the firstdirection. For example, a minimum number of lines can in someembodiments be three lines, but in many practical implementations alarger number of lines can be used, such as four, five, six, ten or morelines, when counting the first, the last and the intermediate lines. Insome embodiments of the invention, the number of lines is modified tomodify the energy distribution, while the effective spot is travellingalong the surface area where fusion of the building material is to takeplace.

In some embodiments of the invention, the primary spot is displaced witha higher velocity along said at least one intermediate line than alongsaid first line and last line. This is often preferred in order toachieve an adequate energy distribution in said first direction, atleast during a portion or a substantial portion of the process. Thehigher velocity of the beam when moving along the intermediate lines, orat least when moving along one or some of them, compensates for the factthat the beam moves along said intermediate lines twice as often as itmoves along the first and last lines. For example, the velocity of theprimary spot along the intermediate lines can in some embodiments of theinvention be about twice the velocity of the primary spot along thefirst and/or last lines. The velocity can be different for differentintermediate lines. The velocity for each line can be chosen inaccordance with a desired energy distribution in the first direction.Now, the velocity with which the effective spot is displaced alongdifferent lines or segments of the scanning pattern can be dynamicallymodified while the effective spot is travelling along the area wherefusion of the building material is to take place, for example, to adaptthe energy distribution to optimize the way in which the process istaking place, for example, in order to increase the quality of theproduct.

In some embodiments of the invention, the scanning pattern furthercomprises lines extending in said first direction, between the ends ofthe first, last and intermediate lines, whereby the primary spot followssaid lines extending is said first direction when moving between saidfirst line, said intermediate lines and said last line. In someembodiments of the invention, the primary spot is displaced with ahigher velocity along said lines extending in the first direction, thanalong said first line and said last line, at least during part of theprocess.

In some embodiments of the invention, the beam is displaced along saidfirst scanning pattern without switching the beam on and off and/orwhile maintaining the power of the beam substantially constant. Thismakes it possible to carry out the scanning at a high speed withouttaking into account the capacity of the equipment, such as a laserequipment, to switch between different power levels, such as between onand off, and it makes it possible to use equipment that may not allowfor very rapid switching between power levels. Also, it provides forefficient use of the available output power, that is, of the capacity ofthe equipment in terms of power.

The use of electron beams for additive manufacturing is known in theart. The present invention uses a light beam, such as a laser beam,instead of an electron beam. A light beam such as a laser beam ispreferred, due to issues such as cost, reliability, and availability.Appropriate scanning systems are available, for example, based onelectronically controlled reflective means such as mirrors. In someembodiments of the invention, the power of the laser beam is higher than1 kW, such as higher than 3 kW, higher than 4 kW, higher thatn 5 kW orhigher than 6 kW, at least during part of the process. Traditionally,when a primary laser spot is raster scanned to fill the region of thebuilding material to be fused, lasers having powers in the order of 400W have often been used. With the present approach, based on the creationof a larger effective laser spot, higher powers can be used, whereby theproductivity can be enhanced.

In some embodiments of the invention, the first scanning pattern can beimplemented in line with the teachings of WO-2014/037281-A2, forexample, in line with the teachings in relation to FIGS. 9-11 thereof.

Another aspect of the invention relates to a system for producing anobject by additive manufacturing, the system comprising

means for supplying building material, and

means for producing a light beam, such as a laser beam, for selectivelyfusing the building material so as to progressively produce the objectout of the fused building material. The system comprises a scanner forscanning the light beam in at least two dimensions. The system isarranged, such as programmed, for carrying out the method describedabove.

For example, the system can comprise a work table on which athree-dimensional object/product is to be built, a powder dispenserwhich is arranged to lay down a thin layer of powder on the work tablefor the formation of a powder bed, a device producing a beam for givingoff energy to the powder whereby fusion of the powder takes place, meansfor controlling the beam across the powder bed for the formation of across section of the three-dimensional product through fusion of partsof said powder bed, and a computer in which information about successivecross sections of the three-dimensional product is stored, which crosssections build the three-dimensional product. The computer controls themeans for guiding the beam across the powder bed to form the crosssection of the three-dimensional object, and the object is formed bysuccessive fusion of successively formed cross sections from powderlayers successively laid down by the powder dispenser.

In some embodiments of the invention, the means for supplying buildingmaterial comprise a powder spraying head comprising a frame defining anopening, the scanner being arranged in correspondence with said frame soas to scan the beam in two dimensions through said opening, the powderspraying head being arranged for distributing the building material inpowder form in correspondence with said opening so that the buildingmaterial can be selectively fused by the beam as it is beingdistributed. This arrangement is practical and allows for a controlleddeposition and fusing of the building material. Suction means can beincorporated to remove the powder that has not been fused.

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a betterunderstanding of the invention, a set of drawings is provided. Saiddrawings form an integral part of the description and illustrateembodiments of the invention, which should not be interpreted asrestricting the scope of the invention, but just as examples of how theinvention can be carried out. The drawings comprise the followingfigures:

FIG. 1 is a schematic perspective view of a system in accordance withone possible embodiment of the invention, adapted for powder bed fusion.

FIG. 2 schematically illustrates an example of the two-dimensionalenergy distribution.

FIG. 3A is a schematic perspective view of a part of a system inaccordance with another possible embodiment of the invention.

FIG. 3B is a top view of the powder spray head of the system inaccordance with the embodiment of FIG. 3A.

FIGS. 4A-4C schematically illustrate three different powder spray headsin accordance with three different embodiments of the invention.

FIGS. 4D and 4E illustrate how the powder spray head can be associatedto the scanner allowing the two parts to be displaced jointly inrelation to an object being produced.

FIG. 5 schematically illustrates an effective spot created by a scanningpattern comprising a plurality of parallel lines.

FIGS. 6A and 6B illustrate one possible scanning pattern comprising aplurality of parallel lines.

FIGS. 7A and 7B illustrate a scanning pattern for creating an effectivespot in accordance with an embodiment of the invention.

FIGS. 8A and 8B illustrate a scanning pattern for creating an effectivespot in accordance with another embodiment of the invention.

FIGS. 9A-9C illustrate scanning patterns according to other embodimentsof the invention.

FIG. 10 schematically illustrate an effective spot in accordance withone possible embodiment of the invention.

FIGS. 11A-11D schematically illustrate different two-dimensional energydistributions of an effective spot in accordance with an embodiment ofthe invention.

FIGS. 12A-12G schematically illustrate how the two-dimensional energydistribution of an effective spot is dynamically adapted during a sweepof the effective spot along a track, in accordance with an embodiment ofthe invention.

DESCRIPTION OF WAYS OF CARRYING OUT THE INVENTION

FIG. 1 schematically illustrates an SLS system in accordance with onepossible embodiment of the invention, for producing an object out of abuilding material that is supplied in powder form, such as metal powder.The system comprises a laser equipment 1 for producing a laser beam 2,and a scanner 3 including two mirrors or similar for two-dimensionalscanning of the laser beam 2 in the horizontal (X-Y) plane. Theequipment for producing a laser beam can, in some embodiments of theinvention, be an equipment suitable for producing laser beams having arelatively high power content, such as 1 kW or more. One example of asuitable device is the Ytterbium Laser System Model YLS-6000-CT-Y13, byIPG Photonics, with a nominal power of 6 kW.

The system further comprises an arrangement for distribution of thebuilding material, comprising a table-like arrangement with a topsurface 101 with two openings 102 through which the building material isfed from two feed cartridges 103. In the center of the top surface 101there is an additional opening, arranged in correspondence with aplatform 104 which is displaceable in the vertical direction, that is,in parallel with a Z axis of the system. Powder is supplied from thecartridges 103 and deposited on top of the platform 104. Acounter-rotating powder leveling roller 105 is used to distribute thepowder in a layer 106 having a homogeneous thickness.

The laser beam is projected onto the layer 106 of the building materialon top of the platform 104 to fuse the building material in a selectedregion or area 11, which corresponds to a cross section of the objectthat is being produced. Once the building material in this area 11 hasbeen fused, the platform is lowered a distance corresponding to thethickness of each layer of building material, a new layer 106 ofbuilding material is applied using the roller 105, and the process isrepeated, this time in accordance with the cross section of the objectto be produced in correspondence with the new layer.

Traditionally, fusing was carried out by scanning the laser beam overthe area 11 to be fused, for example, by making the projected laser spotfollow a plurality of parallel lines extending across the area to befused, until the entire selected area had been fused. In accordance withthe present embodiment of the invention, the laser beam (and the primarylaser spot that the beam projects on the building material) isrepetitively scanned at a relatively high speed following a firstscanning pattern (illustrated as a set of lines extending in parallelwith the Y axis in FIG. 1), thereby creating an effective laser spot 21,illustrated as a square in FIG. 1. This is achieved using the scanner 3.This effective laser spot 21 is displaced according to a second scanningpattern, for example, in parallel with a plurality of parallel lines. InFIG. 1, an arrow indicates how the effective laser spot 21 can, forexample, be displaced in parallel with the X axis of the system. FIG. 1illustrates how a portion 11A of the area 11 to be fused has been fusedduring a preceding sweep of the effective laser spot 21 in parallel withthe X axis, whereas another portion 11B is still waiting to be fused.After it has been fused, the platform 104 will be lowered and a newlayer of building material in powder form will be applied.

The displacement of the effective laser spot 21 according to the secondscanning pattern can likewise be achieved by the scanner 3, and/or dueto displacement of the scanner or associated equipment, for example,along tracks (not shown in FIG. 1), such as tracks extending in parallelwith the X axis and/or the Y axis.

In many variants of this embodiment, pre-heating means such as IR lightsources or other heating devices are provided for pre-heating the powderlayer, for example, to a temperature close to the melting point and/orglass transition temperature of the building material, thereby reducingthe power that has to be applied by the laser beam to achieve the fusionof the building material. In other variants of the embodiment, or inaddition to the pre-heating means, preheating can be carried out by aleading portion of the effective laser spot 21.

In some embodiments of the invention, the system can include means 5 fordynamically adapting the size of the primary spot (for example, so as tomodify the two-dimensional energy distribution and/or the size of theeffective laser spot 21) and/or the focus of the laser beam along theoptical axis. This makes it possible to control (such as to vary ormaintain) the size of the primary laser spot while it is being displacedalong the first scanning pattern, and/or while the effective laser spot21 is being displaced in relation to the object being produced. Forexample, the optical focus can be adapted to keep the size of theprimary spot constant while the primary spot is moving over the surfaceof the object being produced (for example, to compensate for varyingdistances between the scanner and the position of the primary laser spoton the object being produced). For example, means for dynamicallyadapting the focus of the laser beam can in some embodiments of theinvention comprise a varioSCAN focusing unit, obtainable from SCANLAB AG(www.scanlab.de).

FIG. 2 schematically illustrates how the effective laser spot 21features a two-dimensional energy distribution where more energy isapplied in some parts of the effective laser spot than in others duringone sweep of the primary laser spot throughout the first scanningpattern. Here, the arrow indicates how the effective laser spot istravelling along a layer of metal powder, whereby the layer features afused portion 11A and a portion 11B that has not yet been fused. Here,more energy is applied in correspondence with the leading portion thanin correspondence with the trailing portion of the effective laser spot21.

FIGS. 3A and 3B illustrate part of the system in accordance with analternative embodiment of the invention, in which the building materialis fed in parallel with the heating thereof using the laser beam and thescanner 3. As illustrated in FIG. 3A, the system comprises an apparatusincluding a processing head 200 comprising a powder supply head 201integrated with the scanner 3, the powder supply head 201 comprising asubstantially rectangular frame 202 in which a plurality of nozzles 203are arranged, the nozzles receiving the building material, typically inthe form of powder, through channels 205 shown in FIG. 3B. Thus, thebuilding material in powder form 204 is ejected through the nozzles 203,forming a relatively thin film or layer of powder, in correspondencewith an opening defined by the frame 202. The scanner 3 projects thelaser beam 2 through this opening, and scans the laser beam to producethe effective laser spot 21, as explained above and as schematicallyshown in FIGS. 3A and 3B. In some embodiments of the invention, thepowder supply head 201 and the scanner 3 are arranged to move together,for example, forming part of one and the same device, which can bedisplaced in relation to the object that is being produced, so thatmaterial is thus selectively applied and fused onto this object, incorrespondence with the areas in which the object is growing as it isbeing produced. In FIGS. 3A and 3B, the scanning pattern isschematically illustrated as a pattern in the shape of a “digital 8”,that is, with three parallel lines interconnected by two lines at theends of the three parallel lines.

FIGS. 4A, 4B and 4C illustrate some different design options for thepowder supply head, corresponding to three different embodiments of theinvention. FIG. 4A illustrates the powder supply head in accordance withthe embodiments of FIGS. 3A and 3B. FIGS. 4B and 4C illustrate somealternative designs. In all of these cases, there is a frame 202defining an opening or channel through which the laser beam can beprojected onto the powder that is ejected through the nozzles 203.Basically, this approach is in line with some of the so-called coaxiallaser and powder nozzles that are known in the art, but with the centralopening being large enough so as to allow for the scanning of the laserbeam 2 in two dimensions, along the first scanning pattern. In someembodiments of the invention, the processing head including the powdersupply head 201 with frame 202 and nozzles 203, as well as the scanner3, can be displaced so as to displace the effective laser spot inrelation to the object being produced. That is, in these embodiments ofthe invention, the scanner can be used to create the effective laserspot with its two-dimensional energy distribution, whereas thedisplacement of the processing head 200 with the powder supply head 201and scanner 3 provides for the displacement of the effective laser spotand the pool. In other embodiments of the invention, the processing head200 can be fixed and the object being produced can be displaced inrelation to the processing head.

The powder supply heads 201 of FIGS. 4A, 4B and 4C all include aplurality of nozzles, arranged to provide a substantiallytwo-dimensional stream of the building material, that is, a stream beingrelatively thin compared to its extension in the other two directions.Instead of a plurality of nozzles, one wider nozzle can be used. In someembodiments of the invention, the means for spraying the powder can beimplemented based on the teachings of US-2011/0168090-A1 andUS-2011/0168092-A1.

The powder supply head can also incorporate suction means 206 forrecovery of powder that has not been fused by the laser beam, asschematically illustrated in FIG. 4B.

FIGS. 4D and 4E schematically illustrate how the processing head 200, inaccordance with one possible embodiment of the invention, can include ascanner 3 placed adjacent to the powder supply head 201, in this case,above it so as to project the laser beam downwards, through the openingin the frame, onto the object 4 that is being produced. The buildingmaterial is being selectively fused by the laser beam while it is beingfed through the nozzles. The processing head 200 is connected toactuators 300 through linkages 301. In this embodiment of the invention,the displacement is based on the parallel manipulator concept. However,any other suitable means of displacement of the processing head can beused. In some embodiments of the invention, it is the object beingproduced that is displaced in relation to the processing head. Also, acombination of these two approaches can be used.

It has been found that it can often be practical to provide a scanningpattern comprising more than two lines arranged after each other in thedirection of travelling of the effective laser spot (that is, thedirection of the relative movement between the effective laser spot andthe object that is being built), such as schematically illustrated inFIG. 5, where the effective laser spot 21 is created by a plurality ofparallel lines, extending in a direction perpendicular to the directionin which the effective laser spot is being displaced in relation to theobject being built (this direction is indicated with an arrow in FIG.5). The lines can have the same or different lengths, and the spacebetween subsequent lines is one of the parameters that can be used tocontrol the two-dimensional energy distribution.

Such a scanning pattern can be created by repetitively scanning theprimary laser spot in the direction perpendicular to the direction inwhich the effective laser spot is travelling, displacing the laser beama small distance between each scanning step, so as to trace two, threeor more parallel lines. Once the primary laser spot has completed thescanning pattern, it will return to its original position and carry outthe scanning pattern once again. The frequency with which this occurs ispreferably high, so as to avoid undesired temperature fluctuationswithin the effective laser spot 21.

The laser beam can be switched off while it is being displaced towards anew line to be followed, and/or between finishing the last line of thescanning pattern and returning to the first line of the scanningpattern. However, switching laser beams on and off requires time, andcan slow down the scanning frequency. Also, the time during which thelaser beam is switched off is time that is lost in terms of efficientuse of the laser for heating and fusing.

FIGS. 6A and 6B illustrate one possible scanning pattern comprisingthree main lines a-c (illustrated as continuous lines) of the scanningpattern, and hatched lines illustrating the path which the laser spotfollows between said lines. In FIG. 6B, the arrows schematicallyillustrate the way in which the primary laser spot travels over thesurface.

Now, this scanning pattern involves a problem in that the heatdistribution will not be symmetric. The same applies if, at the end ofthe pattern, when finishing the last line c (that is, from the head ofthe arrow of line c in FIG. 6B), the laser beam returns vertically toline a.

A more symmetrical energy distribution with regard to the axis parallelwith the direction in which the effective laser spot is being displacedcan be obtained with a scanning pattern as per FIGS. 7A and 7B, likewisecomprising three parallel lines a-c interconnected by the lines dfollowed by the primary laser spot when moving between the threeparallel lines. As illustrated in FIG. 7B, the laser beam, from thebeginning of the first line a, travels as follows: a-d1-b-d2-c-d3-b-d4.

That is, the primary laser spot travels along the intermediate line btwice as often as it travels through the first line and the last line:it travels along the intermediate line b twice for each time it travelsalong the first line a and the last line c. Thereby, a completelysymmetrical scanning pattern can be obtained, in relation to the axisparallel with the direction in which the effective laser spot istravelling.

The energy distribution along this axis can be set by adjusting, forexample, the distance between the lines a-c and the speed with which thelaser beam travels along the lines. By adjusting the speed and/orscanning pattern, the energy distribution can be dynamically adaptedwithout turning the laser beam on and off or without substantiallymodifying the power of the laser beam. For example, if the energy is tobe distributed substantially equally throughout the effective laserspot, the laser beam can travel with a higher speed along theintermediate line b than along the first line a and the last line c. Forexample, the velocity of the primary laser spot along line b can betwice the speed of the primary laser spot along lines a and c. In someembodiments of the invention, the velocity of the effective laser spotalong lines d1-d4 can also be substantially higher than the velocity ofthe effective laser spot along lines a and c.

Thus, tailoring of the energy distribution can be achieved by adaptingthe distribution of the lines, such as the first, last and intermediatelines a-c, and by adapting the velocity of the laser spot along thedifferent segments a-d (including d1-d4) of the scanning pattern. Thedistribution of the segments and the velocity of the segments can bedynamically modified while the effective laser spot is being displacedin relation to the object that is being produced, so as to adapt thetwo-dimensional energy distribution. Also, the scanning pattern can beadapted by adding or deleting segments during the travelling of theeffective laser spot.

The same principle can be applied to other scanning patterns, such asthe scanning pattern of FIGS. 8A and 8B, which includes an additionalintermediate line b. Here, the path followed by the primary laser spots:a-d1-b-d2-b-d3-c-d4-b-d5-b-d6.

FIGS. 9A-9C illustrate some alternative scanning patterns. For example,the first scanning pattern can be a polygon such as the triangle of FIG.9A, the rectangle of FIG. 9B, and the octagon of FIG. 9C.

FIG. 10 schematically illustrates an effective spot 21 in accordancewith one possible embodiment of the invention. The effective spot has asubstantially rectangular configuration, with a height and a width. Thearrow at the top of the figure illustrates the direction in which theeffective spot 21 is being displaced.

The effective spot 21 is obtained by scanning the primary spot 2Aprojected by the beam, following a scanning pattern comprising fiveparallel lines, indicated by the rows of arrows within the effectivespot 21. In this embodiment, a leading portion 21A of the effective spotprovides a certain pre-heating of the building material, and a trailingportion 21C is provided to slow down the cooling process. The actualfusion of the material takes place in the central portion 21B of theeffective spot 21, that is, between the leading portion 21A and thetrailing portion 21C. This central portion 21B corresponds to the pool.That is, as explained above, contrary to what was generally the case inprior art systems, in this embodiment the pool has a two-dimensionalconfiguration with a size substantially larger than the one of theprimary spot, and the pool does not travel with the primary spot 2Aalong the first scanning pattern, but rather with the effective spot 21.The size and/or the shape of the effective spot 21 and/or of the pool21B can be dynamically adapted during the displacement of the effectivespot along the track followed by the effective spot 21, for example,taking into account the configuration of the object to be produced inthe region where heating is taking place.

FIGS. 11A-11D schematically illustrate different two-dimensional energydistributions of an effective spot in accordance with an embodiment ofthe invention. For example, FIG. 11A illustrates an effective spotfeaturing three bands extending across the effective spot, in thedirection perpendicular to the direction of travelling of the effectivespot. These three bands represent areas with high energy density. Thefirst band may be intended to provide for pre-heating of the material tobe fused, the second band may be intended to provide for the actualfusion, and the third band may be intended for post-treatment of thefused material, for example, to relieve tensions. Other energydistributions are schematically shown in FIGS. 11B-11D. Thetwo-dimensional energy distribution can be adapted dynamically, forexample, adding or removing bands with high energy density, etc. Forexample, FIG. 11F illustrates a two-dimensional energy distribution withenhanced energy density towards the sides of the effective spot. Thiscan often be preferred in order to provide for a substantially constanttemperature along the track, in spite of the fact that, for example,heat dissipation away from the track may be higher at the edges of thetrack.

Feedback, such as feed-back based on thermal imaging, can be used totrigger the dynamic adaptation of the two-dimensional energydistribution, for example, so as to achieve and maintain a desiredtemperature distribution in the area being treated.

FIGS. 12A-12G illustrate an example of how the two-dimensional energydistribution of an effective spot 21 can be adapted while the effectivespot is being displaced along a track (in a direction schematicallyillustrated with an arrow in FIG. 12A), over a layer 106 of buildingmaterial. FIG. 12A illustrates how the effective spot 21 is firstapplied to the building material 106 and starts to heat the buildingmaterial, and in FIG. 12B the two-dimensional energy distribution hasbeen modified so that the effective spot has increased in length alongthe track (in the direction of the arrow in FIG. 12A), featuring aleading portion with high energy density so as to provide for a rapidincrease of the temperature of the building material when the leadingportion reaches the building material.

In FIG. 12C, the effective spot 21 has moved along the track also withits trailing edge, and a fused portion 11A of the building material canbe observed behind the effective spot 21.

In FIG. 12D, the effective spot has reached a section of the objectbeing produced in which the portion of the object begins to decrease inwidth, that is, a portion where the track to be fused progressivelybecomes narrower. Here, the two-dimensional energy distribution isdynamically adapted to adapt itself to the dimensions of the portion ofthe object being produced at each moment. As shown in FIGS. 12D and 12E,the two-dimensional energy distribution is adapted so that the effectivespot progressively grows narrower, and in addition, also the edges ofthe effective spot feature an outline corresponding to the shape of theportion being fused. That is, here, the projection of the effective spotonto the building material is substantially wedge-shaped.

In FIG. 12E, the effective spot 21 has reached a position where theobject being built has a portion of constant width. Here, thetwo-dimensional energy distribution is adapted accordingly. Here, theprojection of the effective spot onto the building material 106 becomessubstantially rectangular. In FIG. 12G, the effective spot can be seenmoving further along the track. Thus, it can be seen how the shape ofthe fused material 11A corresponds to the way in which thetwo-dimensional energy distribution of the effective spot has beendynamically adapted as the effective spot 21 has moved along the track.However, the present invention is obviously not limited to this kind ofdynamical adaptations of the effective spot and its two-dimensionalenergy distribution.

In this text, the term “comprises” and its derivations (such as“comprising”, etc.) should not be understood in an excluding sense, thatis, these terms should not be interpreted as excluding the possibilitythat what is described and defined may include further elements, steps,etc.

On the other hand, the invention is obviously not limited to thespecific embodiment(s) described herein, but also encompasses anyvariations that may be considered by any person skilled in the art (forexample, as regards the choice of materials, dimensions, components,configuration, etc.), within the general scope of the invention asdefined in the claims.

The invention claimed is:
 1. A method for producing an object bysuccessive fusing of a building material, the method comprising thesteps of: a) supplying building material to a fusing site; b) generatinga light beam and directing it at a selected spot on the buildingmaterial, creating a primary spot; c) scanning the primary spot of thelight beam in two dimensions in accordance with a first scanning patternestablishing a first effective spot, larger than the primary spot, onthe building material, the effective spot having a two-dimensionalenergy distribution; and d) repeating the first scanning pattern,establishing a second effective spot on the building material displacedfrom the first effective spot in accordance with a second scanningpattern to progressively fuse the building material; whereby the objectis produced.
 2. The method according to claim 1, wherein thetwo-dimensional energy distribution of the effective spot is dynamicallyadapted during displacement of the effective spot on the buildingmaterial, in accordance with the second scanning pattern.
 3. The methodof claim 2, wherein the two-dimensional energy distribution of theeffective spot is dynamically adapted during displacement of theeffective spot along a track, to change the width of the effective spotto correspond with a portion of the object being produced.
 4. The methodaccording to claim 2 wherein adaptation of the two-dimensional energydistribution of the effective spot is carried out by changing the powerof the light beam.
 5. The method according to claim 2 wherein adaptationof the two-dimensional energy distribution of the effective spot iscarried out by changing the first scanning pattern.
 6. The methodaccording to claim 2 wherein adaptation of the two-dimensional energydistribution of the effective spot is carried out by changing thevelocity of the primary spot moving along the first scanning pattern. 7.The method according to claim 1 wherein the size of the primary spot isdynamically adapted during displacement of the primary spot along thefirst scanning pattern and/or during displacement of the effective spoton the object being produced.
 8. The method according to claim 1 whereinthe effective spot has a leading portion with a higher energy densitythan a trailing portion, or the effective spot has a leading portionwith a lower energy density than a trailing portion, or the effectivespot has an intermediate portion with a higher energy density than aleading portion and a trailing portion, or the effective spot has asubstantially constant energy density throughout the effective spot. 9.The method according to claim 1 wherein the mean velocity of the primaryspot along the first scanning pattern is higher than the mean velocityof the effective spot on the building material.
 10. The method accordingto claim 1 wherein the light beam is scanned at a frequency of more than10 Hz in the first scanning pattern.
 11. The method according to claim 1wherein the size of the effective spot is more than 4 times the size ofthe primary spot.
 12. The method according to claim 1 wherein the stepsof the method are carried out repeatedly in a plurality of cycles. 13.The method according to claim 1 wherein steps a) and b) are carried outin parallel.
 14. The method according to claim 1 wherein the firstscanning pattern comprises a plurality of lines.
 15. The methodaccording to claim 14, wherein the lines are substantially parallellines.
 16. The method according to claim 1 wherein the first scanningpattern is a polygon.
 17. The method according to claim 1 wherein thefirst scanning pattern comprises at least three linear segments andscanning of the beam causes the beam to follow at least one of thesegments more frequently than it follows another one of the segments.18. The method according to claim 17, wherein the first scanning patterncomprises at least three substantially parallel lines distributed oneafter the other in a first direction, and extending in a seconddirection, and three lines comprising a first line, an intermediateline, and a last line arranged one after the other in the firstdirection, wherein scanning of the light beam causes the light beam tofollow the intermediate line more frequently than the light beam followsthe first line or the last line.
 19. The method according to claim 17,wherein the first scanning pattern comprises at least threesubstantially parallel lines distributed one after the other in a firstdirection, and extending in a second direction, the three linescomprising a first line, an intermediate line, and a last line arrangedone after the other in the first direction, wherein scanning of thelight beam causes the light beam to follow the first line, follow theintermediate line, follow the last line, follow the intermediate line,and follow the first line (a), in that order.
 20. The method accordingto claim 18 wherein the first scanning pattern comprises a plurality ofthe intermediate lines (b), and/or the beam is displaced with a highervelocity along the intermediate line than along the first line and lastline, and/or wherein the first scanning pattern further comprises linesextending in the first direction, between the ends of the first, lastand intermediate lines, the beam following the lines extending in thefirst direction when moving between the first line, the intermediatelines and the last line, and/or the beam is displaced with a highervelocity along the lines extending in the first direction, than alongthe first line and the last line.
 21. The method according to claim 1wherein the light beam is displaced along the first scanning patternwith the power of the light beam substantially constant.
 22. The methodaccording to claim 1 wherein the light beam creates a melt poolcorresponding to the effective spot, the melt pool being displaced inaccordance with the displacement of the effective spot on the buildingmaterial.
 23. The method according to claim 1 wherein the light beam isa laser beam.
 24. The method according to claim 23, wherein the power ofthe laser beam is higher than 1 kW.